The present invention relates to an induction heating device, such as an induction heating range or a water boiler and a humidifier utilizing induction heating, for use in home, offices, restaurants, or factories.
An induction heating range will be explained as an induction heating device. The induction heating range includes an induction heating coil for generating a high-frequency magnetic field producing eddy currents in an object to be heated, such as a metallic cooking pot 3, placed near the induction heating coil.
A conventional induction heating range will be explained in more detail referring to FIG. 10. As shown in FIG. 10, the range includes a high-frequency inverter 1 having two switching elements (not shown) and an induction heating coil 2 electrically connected to the high-frequency inverter 1.
A high frequency current is supplied from the high-frequency inverter 1 causes the induction heating coil 2 to generate a high-frequency magnetic field producing eddy currents for heating the cooking pot 3. For adjusting and stabilizing the high frequency current, the high-frequency inverter 1 is monitored in a source current supplied to the inverter with a current transformer (not shown). According to a result of the monitoring, the high-frequency current a driving frequency of the switching elements (not shown) is changed, or a duty for driving the elements while the driving frequency is constant. These operations control the output of the high-frequency inverter 1. In addition, the current flowing in the induction heating coil 2 is monitored with the current transformer (not shown), and the output of the high-frequency inverter 1 is controlled according to a result of the monitoring. For example, the output may be suppressed for reducing a load to the switching elements if the cooking pot 3 is made of non-magnetic stainless steel.
When the cooking pot 3 to be heated is made of non-magnetic metal, such as aluminum or copper, the conventional induction heating range allows the cooking pot 3 to be affected by a counter force of a magnetic field. Containing material having a decreasing overall weight, or receiving an increasing heat, the cooking pot 3 may displace laterally, and may be buoyed from a top plate 4. FIG. 11 illustrates a profile of the relationship between an input power and a buoyant force when the cooking pot 3 of the non-magnetic metal is heated. In FIG. 11, the horizontal axis represents a the power input to the high-frequency inverter 1 while the vertical axis represents the buoyant force exerted on the cooking pot. As shown in FIG. 11, the more the input power, the more the buoyant force increases. In other words, when the buoyant force exceeds the weight, the cooking pot is displaced or buoyed.
For eliminating the foregoing drawbacks, some techniques are disclosed in Japanese Patent Laid-Open Publications No.61-128492 and No.62-276787, in which weight sensors are used for detecting displacement of cooking pots. Japanese Patent Laid-Open Publications No.61-71582 and No.61-230289 disclose a magnetic sensor and a resonant frequency measuring unit, respectively, for detecting the displacement. However, the conventional techniques disclosed in the above publications necessarily include the sensors for detecting the displacement of cooking pots, such as the weight sensor, the magnetic sensor, and the frequency measuring unit, thus increasing the overall cost of production or the number of components.
An induction heating device prevents an object to be heated from being displaced or buoyed due to a magnetic field generated by an induction heating coil. The displacement and buoyancy is prevented by either a source current detector for controlling a high-frequency inverter and an output detector for examining data about a magnitude of an output, such as heating coil current or voltage, of the high-frequency inverter. The induction heating device hence has a simple structure and is inexpensive even if including some extra components. The heating device has a small number of components and can thus has an improved operational reliability.
The induction heating device includes an induction heating coil for generating a high frequency magnetic field to heat an object to be heated, an inverter for supplying a high frequency current to the induction heating coil, an output detector for detecting a magnitude of an output of the inverter, a displacement detector for detecting a displacement of the object based on a change against time of the magnitude of the output of the inverter detected by the output detector, and a controller for controlling the output of the high-frequency inverter according to a result of detection of the displacement detector.